1. Field of Invention
The present invention relates to a light-emitting diode chip (LED chip), and particularly to an LED chip capable of preventing from electrostatic discharge damage.
2. Description of the Related Art
In recent years, LEDs are widely applied, particularly in traffic light apparatuses, large-sized display boards or light source for flat panel displays. To prevent an LED from electrostatic discharge damage (ESD damage), a common solution is use an extra diode, for example a Zener diode, that is reverse and parallel connected to the LED. When an electrostatic discharge occurs, the electrostatic high-voltage characteristic enables the diode, used for avoiding static electricity, to operate in a breakdown voltage zone thereof. In this way, the diode which is reverse and parallel connected to the LED can effectively prevent the LED from ESD damage.
FIG. 1A is a diagram of a conventional flip-chip packaged LED chip and FIG. 1B is a diagram of the LED circuit in FIG. 1A. Referring to FIGS. 1A and 1B, a conventional flip-chip packaged LED chip 100 includes an LED 110 and a diode 120. The LED 110 includes a substrate 112, an N-type doped semiconductor layer 114, an active layer 116, a P-type doped semiconductor layer 118, a transparent conductor layer 119, an electrode 1 and an electrode 2. The above-mentioned N-type doped semiconductor layer 114 is disposed on the substrate 112, while the active layer 116 is disposed between the N-type doped semiconductor layer 114 and the P-type doped semiconductor layer 118. In addition, the electrode 1 and the transparent conductor layer 119 are disposed on the P-type doped semiconductor layer 118, while the electrode 2 is disposed on the N-type doped semiconductor layer 114.
The above-described diode 120 includes an N-type doped region 122 and a P-type doped region 124. The LED 110 is electrically connected to the N-type doped region 122 and the P-type doped region 124 of the diode 120 through solders W1 and W2. In other words, the LED 110 is reverse and parallel connected to the diode 120 (as shown in FIG. 1B); the electrode 1 of the LED 110 and the N-type doped region 122 of the diode 120 are electrically coupled to an operation voltage V1; the electrode 2 of the LED 110 and the P-type doped region 124 of the diode 120 are electrically coupled to an operation voltage V2.
When an electrostatic discharge occurs, the electrostatic high-voltage characteristic enables the diode 120 to operate in a breakdown voltage zone thereof and the static charges would pass through the diode 120 instead of passing through the LED 110. Hence, the static charges are conducted by the diode and expelled from the LED chip 100, and the LED 110 is protected from an electrostatic damage by using the diode 120.
The above-described flip-chip packaged LED chip 100 needs an extra semiconductor substrate to fabricate the diode 120, followed by welding them (the LED 110 and the diode 120) though the solders W1 and W2, which requires a higher production cost.
FIG. 2A is a diagram of another conventional LED chip and FIG. 2B is a diagram of the LED circuit in FIG. 2A. Referring to FIGS. 2A and 2B, a conventional LED chip 200 includes a substrate 210, an unintentionally-doped layer 220, an N-type doped semiconductor layer 230, an active layer 240, a P-type doped semiconductor layer 250, a transparent conductor layer 251, a first metal layer 260, a first oxidation layer 261, a second metal layer 270, a second oxidation layer 271, an electrode 3 and an electrode 4.
The above-mentioned unintentionally-doped layer 220 is disposed on the substrate 210, while the N-type doped semiconductor layer 230 is disposed on the unintentionally-doped layer 220. In addition, the active layer 240 is disposed between the P-type doped semiconductor layer 250 and the N-type doped semiconductor layer 230; the electrode 3 and the transparent conductor layer 251 are disposed on the P-type doped semiconductor layer 250; and the electrode 4 is disposed on the N-type doped semiconductor layer 230. It is noted that, the electrode 3 is electrically connected to the unintentionally-doped layer 220 through the first metal layer 260 in the via hole H1 and the first oxidation layer 261 is disposed on the sidewall of the via hole H1. The first oxidation layer 261 enables the first metal layer 260 being insulated from other film layers (the N-type doped semiconductor layer 230, the active layer 240 and the P-type doped semiconductor layer 250).
The above-described electrode 4 is connected to the unintentionally-doped layer 220 through the second metal layer 270 in the via hole H2. The second oxidation layer 271 is disposed on the sidewall of the via hole H2 and enables the second metal layer 270 being insulated from the N-type doped semiconductor layer 230. It should be noted that, there is a Schottky contact between the first metal layer 260 and the unintentionally-doped layer 220 and between the first metal layer 260 and the unintentionally-doped layer 220, respectively. In addition, the electrode 3 is electrically coupled to the operation voltage V1, while the electrode 4 is electrically coupled to the operation voltage V2.
When an electrostatic discharge occurs, the electrostatic high-voltage characteristic enables the diode 202 (as shown in FIG. 2B) to operate in a breakdown voltage zone thereof and the static charges would flow through the diode 202. In other words, the static charges would sequentially flow through the electrode 4, the second metal layer 270, the unintentionally-doped layer 220, the first metal layer 260 and the electrode 3. In this way, the static charges will not flow into the LED 201 so that the diode 202 can protect the LED 201 from electrostatic damage.
However, the first metal layer 260 and the second metal layer 270 of the LED chip 200 must be electrically insulated from the film layers except for the unintentionally-doped layer 220, the electrode 3 and the electrode 4. Therefore, the first oxidation layer 261 and the second oxidation layer 271 formed on the sidewall of the via hole H1 and the via hole H2, respectively, are necessary by the prior art. As a result, a new problem arises that, the deeper the via holes H1 and H2, the more difficult to form the first oxidation layer 261 and the second oxidation layer 271 in the via holes H1 and H2. In other words, the production yield becomes worse.
FIG. 3A is a diagram of a further conventional LED chip and FIG. 3B is a diagram of the LED circuit in FIG. 3A. Referring to FIGS. 3A and 3B, an LED chip 300 is formed by an LED 301 and a diode 302. The LED 301 includes a substrate 310, an N-type doped semiconductor layer 320, an active layer 330, a P-type doped semiconductor layer 340, a transparent conductor layer 350, an electrode 5 and an electrode 6.
The above-mentioned N-type doped semiconductor layer 320 is disposed on the substrate 310, while the active layer 330 is disposed between the P-type doped semiconductor layer 340 and the N-type doped semiconductor layer 320. Besides, the transparent conductor layer 350 and the electrode 5 are disposed on the P-type doped semiconductor layer 340, while the electrode 6 is disposed on the N-type doped semiconductor layer 320.
In addition, the diode 302 is disposed on the substrate 310 and includes a P-type doped region 362, an N-type doped region 364, an electrode 7 and an electrode 8. The electrode 7 is disposed on the P-type doped region 362, while the electrode 8 is disposed on the N-type doped region 364. In addition, the electrodes 5 and 8 are electrically coupled to an operation voltage V1 through a conductive wire, while the electrodes 6 and 7 are electrically coupled to an operation voltage V2 through another conductive wire. In other words, the diode 302 is reverse and parallel connected to the LED 301 (as shown in FIG. 3B).
When electrostatic discharge (ESD) occurs, the electrostatic high-voltage characteristic enables the diode 302 (as shown in FIG. 3B) to operate in a breakdown voltage zone thereof and the static charges would pass through the diode 302 instead of passing through the LED 301. Hence, the LED 301 is protected from electrostatic discharge damage. However, to connect the electrode 5 to the electrode 8, a long conductive wire is required and an excessive long wire would deteriorate the reliability of the LED chip 300. In addition, since the diode 302 occupies a partial area of the substrate 310, therefore the usable light-emitting area of the LED 301 is relatively decreased, which affects the LED brightness.